Do you intend to pre-order when they start on Tuesday, wait until later, or don't plan to pre-order at all?
What is influencing your decision?
Do you have faith in the developers that you will enjoy the expansion and so have no reservations pre-ordering as soon as possible?
Do you not have faith in them and so have no desire to pre-order?
Are you a collector/completionist only pre-ordering because you will go crazy if you miss out on the pre-order bonuses to fill those collector/completionist impulses?
Will you only pre-order because there is no risk to you and so why not?
I'm pre-ordering because I have faith in the development team. I've no doubt that Dawntrail will have its flaws just as each expansion has had some but I'm also confident I will still enjoy playing the expansion.